Air treatment apparatus

ABSTRACT

An air extraction and treatment unit ( 2 ) is located above a source of contaminated air. The apparatus has a series of ultraviolet tubes ( 20 ) for treating the decontaminated air. The unit is arranged such that in use substantially no direct or reflected ultraviolet light is visible from outside the unit. Furthermore even when a removable filter ( 4 ) is removed, there is no direct line of sight to the ultra-violet sources.

This invention relates to apparatus for treating contaminated air suchas is produced in commercial kitchens, e.g. to remove odours and thelike therefrom.

The usual way to treat air laden with grease and odours which isproduced by a cooking appliance is to extract air from above theappliance to the outside by means of an extraction unit mounted abovethe appliance. This extraction unit is generally in the form of a hoodand includes a number of filters and/or particle traps to trap greaseand other particles in the air. Some sort of deodorising means is alsooften included such as an activated carbon filter or a source offragrant masking oil.

The problems with mechanical filters are that they tend to need regularreplacement or cleaning and also that when laden with grease etc., theyrepresent a significant fire hazard.

Proposals have been made to use ultra-violet light to decontaminate airin air extraction units of the type described above although it isunderstood that to date none has progressed beyond the prototype stage.In these arrangements ultra-violet tubes are provided above the airinlet behind the front wall of the unit. This front wall therefore hidesthe tubes from direct view. However since these units are fabricatedfrom stainless steel, when the tubes are in operation light from themescapes through the air inlet and is reflected off the downwardlyextending rear wall of the unit, thus making the light clearly visible.

The inventors have realised however that even reflected light from theUV tubes typically used in these applications is hazardous despite theprevious tacit assumption to the contrary.

When viewed from a first aspect therefore the present invention providesan air extraction and treatment unit for mounting above a source ofcontaminated air, said unit comprising an air inlet through which saidcontaminated air is extracted in use, an air outlet through whichdecontaminated air is expelled in use, and an air treatment meansdisposed therebetween, said air treatment means having an ultra-violetlight source, wherein the unit is arranged such that in usesubstantially no direct or reflected ultra-violet light is visible fromoutside the unit.

Thus it will be seen that in accordance with the invention, the hazardsof exposure even to reflected ultra-violet (UV) light are substantiallyavoided. This means that such units can safely be employed at the sourceof contaminated air e.g. at a cooking appliance in a commercial orindustrial kitchen even though someone may need to work very close tothe unit whilst using the appliance. A person working in the vicinity ofthe unit will not necessarily even know that it contains a potentiallyhazardous UV radiation source. In accordance with the invention noparticular special precautions need be taken.

Air is typically moved through units of the type to which the inventionapplies by a remote fan downstream of the unit, e.g. just before thedecontaminated air is exhausted to the atmosphere. Commonly a singlesuch fan will serve several air extraction and treatment units.

The unit may be arranged just with suitably positioned walls to avoidthe escape of light from the unit. This is relatively easy to achievefor most of the walls of the unit. Of course however the air inlet mustbe in fluid communication with the exterior of the unit and thereforeparticular precaution is necessary to avoid the potential escape of UVlight from any angle which might render it visible to a user. The regionof the air inlet may be therefore be defined with suitably positionedwalls.

In preferred embodiments however a filter disposed in the path ofincoming air forms at least part of the barrier to light escaping. Thisfilter is preferably arranged to remove relatively large particles, e.g.grease and/or fat, from the air passing through it. This is particularlybeneficial since the inventors have realised that UV light is mostefficient at removing odours as opposed to particles of fat and greaseand furthermore that its efficiency at removing odours is enhanced ifthe grease and fat has already been removed from the air being treated.

In the most preferred embodiment the filter is of the type which forcesair flowing therethrough to change direction abruptly. This arrangementhas been found to be best for removing larger particles of fat andgrease by means of a centrifuge effect without clogging the filter. Mostpreferably the filter is reusable and therefore requires at mostperiodic cleaning.

The filter may be permanently or semi-permanently fixed, i.e. with theintention that it is not removed by an ordinary user. Preferably thoughthe filter is removable, e.g. for cleaning. As stated above, inpreferred embodiments the filter provides at least part of the barrieragainst the escape of UV light. It follows therefore that if it isremoved there will no longer be such a barrier. The inventors haverealised that whilst direct UV light of the sort used to deodorise aircan be hazardous with only brief exposures, light reflected fromstainless steel parts is hazardous only with longer exposures.

Thus where the unit comprises a removable filter providing at least partof the light barrier, the rest of the unit is preferably arranged suchthat even with the filter removed no direct UV light from the unit isvisible, i.e. only reflected light is visible.

Such a feature is considered to be inventive in its own right. Viewedfrom a second aspect therefore, the invention provides an air extractionand treatment unit for mounting above a source of contaminated air, saidunit comprising an air inlet through which said contaminated air isextracted in use, an air outlet through which decontaminated air isexpelled in use, a removable air filter disposed in the path of incomingair, and an air treatment means disposed downstream of the air filterand having an ultra-violet source, wherein when the air filter isremoved there is no direct line of sight between the ultra-violet sourceand the outside.

Thus exposure to direct UV light can be avoided at the time of filterremoval.

It will be appreciated that references herein to a removable filtercover at least both a filter which can be fully removed, e.g. formachine washing, and a filter which is removed from its normal operatingposition but is not fully detached from the rest of the unit, e.g. byhinging open for manual cleaning in situ.

It is further preferred that means are provided to reduce or interruptthe supply of power to the UV source in the event that such a filter isremoved. Additionally or alternatively means are provided to interruptor reduce the power in the event that any part of the unit isdismantled.

The means for interrupting or reducing the power may comprise a switchsuch as a microswitch or the like in the region of the removable filteror other removable part of the unit, but preferably comprises pressuresensing means which can sense the drop in pressure inside the unit ifthe filter or any other part is removed. This is beneficial since itmeans that the UV source can be switched off if any leak develops—evenif not associated with an intentionally removable part.

In the preferred arrangement in which there is both a power supplyreduction or interruption when the filter is removed, and no direct lineof sight between the UV source and the outside, if there is a delay ormalfunction in the operation of the former safety feature, the latterprovides an additional safety feature.

It is also a preferred feature of the present invention that a baffle isprovided which is arranged to direct incoming air across the whole areacovered by the UV light source or sources. In one convenient embodimentit is this baffle which prevents direct light from the UV sourceescaping from the unit even when a removable filter is removed.

Downstream of the filter, there may be provided means to cause one ormore further changes in the direction of air flow, to provide anadditional fat and grease removal effect. Such means may comprise thebaffle mentioned above.

Certain preferred embodiments of the present invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

FIG. 1 is a cross-sectional view of an air extraction and treatment unitin accordance with the present invention;

FIG. 2 is the same view of FIG. 1 except for the removal of referencenumerals for clarity and the addition of air flow arrows;

FIG. 3 is a cross-sectional view of the same unit as in FIGS. 1 and 2with the filter removed; and

FIG. 4 is a cross-sectional view of a second embodiment of theinvention.

Turning to FIG. 1, this shows a cross-section through an air extractionand treatment unit which is installed above a cooker in a commercialkitchen (not shown). The unit is generally encased in a stainless steelhousing 2 which is attached to a wall along its rear wall 2 a. A greasefilter 4 is arranged towards the front of the unit. The filter hasrespective upper and lower extensions 4 a, 4 b which are received incorresponding slots 6 a, 6 b formed in the unit housing. The greasefilter 4 has an air inlet opening 8 and an internal baffle 10 whichdepends from the rear edge of the opening 8. It will be seen from FIG. 1that when the grease filter 4 is installed in the position shown, itcovers the opening 12 in the lousing of the unit which would otherwisebe present.

Between the opening 12 and the rear wall 2 a of the housing there isdefined a plenum 18. A baffle 14, which is fixed to a short extension 16of the wall defining the opening 12, extends into the plenum 18. Thebaffle 14 is bent so as to direct air entering the plenum diagonallydownwardly. At the top of the plenum 18 is an array of UV tubes 20 whichare held in a cassette 22. The cassette 22 is slidably received in frontand rear brackets 24, 26 respectively. A series of clips (not shown) isprovided to hold the cassette 22 in place. Electrical connection to thetubes is made by means of a removable electrical connector 28 andelectrical supply cable 30.

Above the UV cassette 22 is a further space 32 which communicates withan air outlet duct 34. The front of the space 32 is delimited by a wall36 which, in conjunction with the forward UV cassette 24 and a similarwall 38 defining part of the lower plenum 18, defines a front accessspace 40 separated from the air flow in which the electrical connector28 and cable 30 are housed. The front panel 42 which provides access tothis space is secured to the main housing 2 of the unit by means of aseries of special screws 44 (shown only schematically). These screwshave specially shaped heads in order to ensure that only qualifiedservice personnel possessing the right tool are able to remove the panel42 and therefore gain access to the UV cassette 22.

Finally, a pressure sensor 46 is disposed in the plenum 18 adjacent theupper slot 6 a for receiving the grease filter 4. This sensor iselectrically connected to a control device (not shown) for switching offthe electrical supply to the UV cassette 22 in the event that a drop inpressure in the plenum 18 is detected. This will arise for example ifthe grease filter 4 is removed or if the front panel 42 is removed sincethe enclosed space 40 is not pressure-sealed from the plenum 18 or space32.

Operation of the unit will now be described. Reference is made to FIG.1, but also to FIG. 2 which is the same as FIG. 1 but with the referencenumerals omitted for clarity and the pattern of air flow marked on.

A fan (not shown) downstream of and in fluid is communication with theair outlet duct 34 creates a large negative pressure in the unit whichsucks air through it. Air emanating from the cooker and laden withgrease, fat and other organic substances is therefore drawn upwardly andthrough the air inlet opening 8 in the grease filter 4. The air isforced to flow around the internal baffle 10 in the grease filter and inparticular around the sharp angled bend 10 a at the lower end thereof.This sharp change of direction causes larger particles of grease as fatto be thrown out of the air stream and into the recess 4 b in the greasefilter.

The collected grease/fat will tend to remain molten due to therelatively high temperature of the walls of the grease filter andtherefore drains through the discharge hole 48 into a recess 50 in themain housing.

Although not visible from the Figures, the recess 50 is inclined in alongitudinal direction so that the molten grease and fat collects in adesignated sump and may be easily removed. Again, the relatively hightemperature of the metal walls of the recess 50 keep the grease/fatmolten.

Once the air has passed around the distal end 10 a of the internalbaffle 10, it passes back up the rear half of the grease filter 4 andexits through the opening 12 into the main plenum 18. The baffle 14disposed in this plenum directs the air diagonally downwardly towardsthe bottom rear corner of the plenum 18. However, the negative pressureinduced by the fan draws the air generally upwardly and therefore causesit to curl around the distal edge of the baffle 14 and towards the UVtubes 20. The air is drawn over the surfaces of the UV tubes 20.

The UV light causes ozone to be generated from oxygen present in the airand the ozone proceeds to oxidise the organic contaminants present inthe air. The UV radiation also breaks down the larger organic substancesthrough the process of photolysis. These processes are highly effectiveat removing odours from the air. Once odours and other organicsubstances have been removed, the air passes up into the space 32 andthen through the outlet duct 34 from which it may be exhausted safely tothe atmosphere.

It may clearly be seen from FIGS. 1 and 2 that not only is it impossibleto trace a direct light path from any of the UV tubes to the regionoutside the unit, nor can any such path be traced for light reflectedfrom the rear wall 2 a, lower wall 2 b or indeed any other part of theapparatus.

Turning now to FIG. 3, the same air extraction and treatment unit isshown as in FIGS. 1 and 2, except that this time the grease filter 4 hasbeen removed. If this is done whilst the unit is still operational, thepressure sensor 46 will sense the resultant drop in pressure and cut thesupply of electrical power to the UV tubes 20. However, as may clearlybe seen, even if the power to the UV tubes 20 were not to be cut for anyreason, the internal baffle 14 prevents any direct line of sight betweenthe opening 12 and the UV tubes 20, although it is now possible througha small angle to see the back wall 2 a of the plenum 18 and thereforeany light reflected from this. However, a warning sticker (not shown)warns the user to switch off the unit if this area should becomevisible. With the filter 4 removed, the user may gain access to theplenum 18 to clean it periodically. Since the result of the UV oxidationprocess is fine, dry dust, cleaning is relatively straightforward.

In order to clean or replace any of the UV tubes, an authorised serviceperson possessing the right tool must use it to undo the special screws44 and remove the front panel 42. The electrical connector 28 may thenbe removed from the UV cassette 20 and the clips (not shown) retainingthe cassette 22 in may be undone. This allows the cassette 22 to be slidout horizontally from the brackets 24, 26 to allow the tubes to becleaned with a damp cloth and/or replaced.

A second, preferred embodiment of the invention is shown in thecross-sectional view of FIG. 4. This embodiment is substantially similarto the first and thus only the differences therebetween will bementioned.

The first difference is that there is no inclined wall extending fromthe rear of the lower slot 6 b to form the opening 12 as there is inFIGS. 1 to 3. Instead, a series of vertical spacers 52 is provided atlongitudinally spaced intervals along the apparatus and which extendbetween the upper and lower slots 6 a and 6 b. The longitudinal gapsbetween the spacers 52 are slightly shorter than the width of individualfilter units 4 such that the filters 4 overlap the spacers 52 at theedges thereof. The cross-section in FIG. 4 is taken at one such point.This overlapping arrangement further ensures that no direct or reflectedUV light from the UV tubes 20 is able to escape from the front of theapparatus.

Secondly a sloping base wall 54 is included, extending from the rear ofthe plenum 2 a to the grease collection channel 50. This wall 54 servesto direct any remaining grease in the chamber 18 into the greasecollection channel 50.

Thirdly the upper baffle 14′ is curved in profile. Furthermore it ismanufactured in longitudinal sections to facilitate removal—e.g. forcleaning etc.

It will be apparent to those skilled in the art that the arrangementsdescribed above are just two of many possible examples of how the unitmay be arranged in order to prevent direct and reflected light fromescaping.

1. An air extraction and treatment unit for mounting above a source ofcontaminated air, said unit comprising an air inlet through which saidcontaminated air is extracted in use, an air outlet through whichdecontaminated air is expelled in use, and an air treatment apparatusdisposed between said air inlet and said air outlet, said unit defininga path between said air inlet and said air treatment apparatus, said airtreatment apparatus having an ultraviolet light source and a barrier insaid path between said ultraviolet light source and said air inlet, saidbarrier for blocking all direct or reflected UV light, wherein the unitis arranged such that in use no direct or reflected ultraviolet lightcan escape or is visible from outside the unit, the unit furthercomprising a removable filter disposed in said path at said air inlet,the unit being arranged such that even with the removable filter beingremoved no direct or reflected UV light from the unit can escape or isvisible whereby no UV light will expose and harm a user.
 2. A unit asclaimed in claim 1, wherein said filter is of the type which forces airflowing therethrough to change direction abruptly.
 3. A unit as claimedin claim 1 comprising apparatus for reducing or interrupting the supplyof power to the UV source in the event that said filter is removed.
 4. Aunit as claimed in claim 1 comprising apparatus for reducing orinterrupting the power supply to said ultra-violet source in the eventthat a part of the unit is dismantled.
 5. A unit as claimed in claim 3wherein said apparatus for reducing or interrupting the power comprisespressure sensing apparatus which can sense a drop in pressure inside theunit if the filter or any other part is removed.
 6. A unit as claimed inclaim 1 comprising a baffle arranged to direct incoming air across thewhole area covered by the UV light source or sources.
 7. A unit asclaimed in claim 4 wherein said apparatus for reducing or interruptingthe power comprises pressure sensing apparatus which can sense a drop inpressure inside the unit if the filter or any other part is removed. 8.A ventilation system comprising: an air inlet having a removable filterdisposed thereabout; an air outlet disposed opposite said air inlet; anultraviolet lamp disposed between said air inlet and said air outlet,said ultraviolet lamp for emitting ultraviolet light at a predeterminedwavelength, said filter forming a barrier to both direct and reflectedlight escaping; and a baffle being disposed between said air inlet andsaid air outlet, said baffle blocking all ultraviolet light emitted fromsaid ultraviolet lamp so that no direct or reflected ultraviolet lightcan escape or is visible from outside said system, said baffle arrangedso that even if said removable filter is removed no direct or reflectedultraviolet light from said system can escape or is visible from outsidesaid system.